function z = preview_input ()

x = -3:0.1:3;
y = -3:0.1:3;

[n m] = size(x);

for i=1:m
    for j=1:m
         z(j,i) = 3*( (1-x(i))^2 )*exp(- x(i)^2 - (y(j)+1)^2 );
    end
end

mesh (x,y,z);
end